Mine roof support assemblies

ABSTRACT

A mine roof support assembly composed of three frames each with two props seated in floor engaging skids interconnected by leaf springs and supporting a roof cap. Shifting rams and guiding devices are provided between the frames to effect shifting of the central frame relative to the outer frames and vice versa. The leaf springs of each frame have spaced apart connection units enabling the frames to be connected to the rams and guiding device in various positions offset longitudinally of the frames. The roof caps have an extendible bar at least at their forward ends and there is a clearing shield with a floor engaging ramp extending across the front of the assembly and connected thereto through further rams.

States eulker et a1.

atet [191 t 1 1 Dec.3,1974

[ MINE ROOF SUPPORT ASSEMBLIES Gewerkschaft Eisenhutte Westfalia, Wethmar near Lunen, Westfalia, Germany 22 Filed: 'May 9,1973

[21] Appl. No.: 358,558

[73] Assignee:

[30] Foreign Application Priority Data May 10, 19 72 Germany 2222801 52] US. (:1. 61/45D [51] Int. Cl. E21d 15/44, E21d 23/00 [58] Field of Search 61/45 D; 299/31, 3'33"" [56] References Cited UNITED STATES PATENTS 3,344,610 10/1967 Dommann 61/45 D 3,431,737 3/1969 Bowey 61/45 D 3/1969 Heyer 61/45 D 3,490,243 1/1970 Groetschel 61/45 D 3,570,255 3/1971 Shuttleworth 61/45 D FOREIGN PATENTS OR APPLICATIONS 1,561,033 2/1969 France 61/45 D.

1,171,944 11/1969 Great Britain 61/45 D Primary ExaminerDennis L. Taylor Attorney, Agent, or Firm-Sughrue, Rothwell, Mion Zinn & Macpeak [5 7] ABSTRACT A mine roof support assembly composed of three frames each with two props seated in floor engaging skids interconnected by leaf springs and supporting a roof cap. Shifting rams and guiding devices are provided between the frames to effect shifting of the central frame relative to the outer frames and vice versa. The leaf springs of each frame have spaced apart con nection units enabling the frames to be connected to the rams and guiding device in various positions offset longitudinally of the frames. The roof caps have an extendible bar at least at their forward ends and there is a clearing shield with a floor engaging ramp extending across the front of the assembly and connected thereto through further rams.

16 Claims, 6 Drawing Figures PATENTEL v 3,851,480

SHEET 2 OF 6 PATENTEU 358 31974 SHEET 30F 6 MINE ROOF SUPPORT ASSEMBLIES assembly and to mineral mining installations employing v such assemblies.

vide an improved form of assembly enabling more advantageous installations to be produced.

SUMMARY OF THE INVENTION According to the invention there is provided a mine roof support assembly composed of relatively displaceable frames, each frame having telescopic props supporting a roof cap and resilient means interconnecting the bases of the props, guiding and shifting means operably disposed between adjacent pairs of frames for effectingrelative displacement of the frames and a plurality of connection .units provided on the resilient means of each frame and spaced apart longitudinally thereof and in the direction of said relative displacement, each connection unit enabling connection to be made between the resilient means and the associated guiding and shifting means with each guiding and shifting means being connected to selected ones of the connection units of the adjacent pair of frames.

Preferably'three frames are provided each with two props, with the central frame being displaceable relativeto the outer frames and vice versa.

In a mining installation, a plurality of such assemblies would be disposed -si'd e-by-side and a mineral cutting machine would be moved across the forward 'ends of the frames to cut mineral, usually coal, from a face. The provision of the connection units for each frame enables the'frames of each assembly'to be staggered, as is particularly useful with curved faces especially at the transition zone between a short heading andj a roadway. With an installation of this type the roof of the'working can be efficiently supported at all times over the entire heading and into the roadway without hindering the other operating parts of the installatioh.

The props of the frames of each assembly can be supported by floor-engaging skids and parallel leaf springs, constituting the aforesaid resilient means, may be connected between these skids. Further leaf springs directed transversally-of the frames preferably serve'to connect the units to the guiding and shifting means and are connected to the selected units by suitable detachable means. v v

To enhance the versatility of the assembly the roof cap of each frame, usually itself of multi-part construction, may have an extendible roof bar at its forward end operated by a piston and cylinder unit. During operation the machine would be moved back and forth in successive cutting and return cycles. The central frame of each assembly would be shifted in turn towards the face and the roof bar extended just after the machine passes in a cutting run or cycle. The outer frames would then be moved up and their roof beams similarly extended. As the machine moves back the central frame and then the outer frames of each assembly would again be shifted but the roof bars are now retracted to resume the initial position. I

Preferably a clearing shield is disposed at the forward end of the assembly and this shield extends across the entire width of the assembly; The shield is movable along the floor of the mine working relative to the assembly to assist, for example, in loading coal onto a drag conveyor connected to the cutting machine. However, the primary purpose of the shield is to ensure that thefloor of the working is maintained reasonably flat and clean in front of the assembly when the frames are moved forwards in accordance with the mining progress. The clearing shield may have a body disposed in a substantially upstanding position and a ramp pivotably connected to said body to move about an axis extending transversally of the direction of displacement and engageable, during use, with the floor of a mine working. I

According to further features of the invention the central frame of each assembly may be shorter in length, in the direction of relative displacement, than the outer frames by adistance corresponding to a shifting step so that when the frames are arranged side-byside with the forward ends of their roof caps aligned the props of the central frame are disposed forwardly of the corresponding props of the outer frames by said distance, there being further provided an extendible roof bar at the rear end of the roof cap of said central frame which, when extended, compensates for said difference in length between the frames. This construction is ad-v I vantageous since the assemblies can be shifted in the manner described and by operating the forward extendible roof bars of the frames and the rear extendible bars of the central frames the ends of the bars can be maintained in alignment thus ensuring the roof is adequately supported over a substantially uniform area.

The invention may bev understood more readily and various otherfeatures of the'invention may become apparent from consideration of the following description.

BRIEF DESCRIPTION OF DRAWINGS Embodiments of the invention will now be described,

by way of examples only, with reference to the accompanying drawings, wherein:

FIG. 1 is a side view of a roof support assembly made in accordance with the invention;

, FIG. 2 is an end view of the support assembly shown in FIG. 1 as viewed from the coal face with the clearing .shield removed;

FIG. 3 is a plan view of the assembly shown in FIGS. 1 and 2 with the roof caps removed; FIG. 4 is a plan view of a short coal face working, employing a support system composed of assemblies of the type shown in FIGS. 1 to 3;

FIG. 5 is a plan view of the working showing the part of the support system in conjunction with a loading device and a drag conveyor; and

FIG. 6 is a view corresponding to FIG. 5 but showing a somewhat modified installation.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring initially to FIGS. 1 to 3, the roof support assembly made in accordance with the invention consists of three individual displaceable frames designated I, II and III. The frames are of identical construction, each being provided with two hydraulically operated telescopic props 10, 11 which, in the known manner, are interconnected at the floor and at the roof. The props 10, 11 of each frame I, II, III rest in a floorengaging skid 13 and the skids 13 of each frame I, II, III are interconnected, in the direction of advance R, by resilient means in the form of two horizontal parallel leaf springs 14, 15 disposed one above the other and connected to the skids 13 with the aid of bolts 16.

The heads of the props 10, 11 of each frame I, II, III carry a multi-part roof-engaging member or cap essentially composed of bars l7, 18 which are flexibly interconnected at a joint 19. A spring device 20 is mounted on the joint 19 to bias the bars 17, 18 towards the roof of the working and prevent the joint 19 from pivoting out of position when the props 10, 11 retract. The roof bar 18 extends by a considerable distance towards the coal face and the extending part 18' of the bar 18 bears a further extension device. This device consists of a pair of displaceable bars 21 which are mounted on the lower side of the roof bar part 18' and a hydraulic piston and cylinder unit 22 which is operable to extend the bars 21 forwards towards the coal face in the direction shown by the arrow R) beyond the outer end of the bar 18 or to retract the bars 21 in the opposite direction so that they rest beneath the bar 18. The unit 22 is disposed in a position inclined in relation to the horizontal. The piston rod of the unit 22 is pivotably connected to the roof bar 18 by means ofa pin 23 and the cylinder of the unit 22 is pivotably connected to the bars 21 by means of a pin 24.

At the stowage or goaf end of the roof bar 17 there is flexibly suspended a rubble deflector 25. This is supplemented by an inclined guard shield 26 displaceably mounted on brackets 28 provided on the props 11 of the outer frames I and III by means of pins 27 engaging invslots. The shield 26 is provided with side walls 29 so that the shield 26 partly surrounds the rear props 11 of the frames I, II, III. Between the central frame II and the two outer frames I and III in each case there is provided a guide and shifting means 30 for relatively displacing the frames I, II and II, III. Each means 30 consists of guide means and shifting means. Each guide means is composed of two parallel bar-like guide elements 31 and 32 (FIG. 2) situated vertically above one another. The two guide elements 31, 32 are interconnected at their ends and the elements 31, 32 are also connected to a protective housing 33 (FIG. 3), containing a slidable guide piece arranged to move along the elements 31, 32 and the housing 33. Each housing 33 has a longitudinal slit enabling connection to be established between the guide piece and the outermost frame I, III.

Each shifting means is in the form of a ram 62 which has its cylinder pivotably connected at a joint 65 to the associated housing 33 and a piston rod 63 likewise pivotably connected at a joint 64 to the rear prop ll of the outermost frame I, III via a bracket or the like.

On each pair of leaf springs 14, 15 there are three connection units 35, 36 and 37 spaced at equal distances apart along the length of the springs 14, 15. These units '35, 36, 37 are essentially composed of plates disposed on the exterior of the springs 14, 15 and vertical cotter pins 40 extending through these plates. The units 35, 36, 37 enable selective connection to be made between the frames and the guide means. As illustrated each unit 36 is connected with two pairs of leaf springs 38, which, as may be seen from FIGS. 1 and 3, are arranged side-by-side and one above another. The leaf springs 38 of the unit 36 on the middle frame II are connected laterally to the housings 33 of the two guide means on either side thereof while the leaf springs 38 of the units 36 on the outer frames I and III are connected with the guide pieces within the housing 33 of the guide means. The adjacent frames I, II and II, III can be relatively displaced in the direction of arrow R by operation of the rams 62 and the guide means (31, 32 etc.) ensures the frames I, II, III move accurately in a direction parallel to the axes of the springs 14,- 15. Provision is made whereby the springs 38 can be connected to any one of the units 35, 36, 37 on each frame I, II, III. In this way the frames I, II, and II] can be staggered in relation to each other, in the direction of travel, by the distance separating the units 35 and 37 of each frame from the central unit 36. Easily detachable connecting devices are provided for the connection of the leaf springs 38 to units 35, 36, 37 or the springs 14, 15. For example, as shown the leaf springs 38 may be connected at the ends with U-shaped sliding spacers 39 which are situated between the parallel leaf springs 14 and 15. The vertical cotter pins 40 can then be used to lock these sliding spacers 39 with the leaf springs 14 and 15.

The assembly I, II, III is also provided, on the coal face side, with a clearing shield 50 extending over the entire width of the assembly. The shield 50 has a hollow body 51 disposed in a substantially vertical position. The height of the body 51 can be adjusted by the addition of further components. A shovel-shaped ramp 52,

inclined at an angle to the floor, is pivotably connected via pins 53, with horizontal axes, to the body 51. The ramp 52 is provided at the rear with upstanding webs 54 which can rest against the rear side of the body 51. In the normal'state the ram 52 rests against the floor and the webs 54 engage on the rear of the body 51. The entire shield 50 can be moved forwards towards the coal face and backwards in an opposite direction by means of two double-acting hydraulic piston and cylinder units 55. The cylinders of these units 55 are pivotably attached at joints 56 to the upper zone of the body 51, and the piston rods 57 of the units 55 are pivotably connected, on the stowage or goaf side, at joints 58 with the housings 33. In order to guide the shield 50 during its displacement two parallel guide rails 59 are provided which are shown as broken lines in FIGS. 1 and 3. The guide rails 59 are preferably in the form of leaf springs arranged on edge and flexibly attached at the joints 60 (FIG. 1) to the body 51. The joints 60 are situated underneath the joins 56 of the units 55, and at a certain distance laterally outwardly therefrom. The guide rails 59, as shown in FIG. 2, are mounted in recesses 61 on either side of the central frame II, i.e., between the central frame II and the guide and shifting means 30. The recesses are defined by guides attached to the frame II and the rails 59 and are displaceable in the direction R.

By operating the two units 55 the clearing shield 50 can be moved forwards in the direction shown by the arrow R, in which process the body 51 is slightly tilted in the vertical plane by the units 55 so that the ramp 52 presses against the floor. The support webs 54 engage at the rear side of the body 51 so that contact between the floor and the ramp 52 is maintained and any material lying in front of the ramp 52 during movement of the shield 50 will be pushed towards the face. If the units 55 are subjected to pressure in the opposite direction the clearing shield 50 is moved back in which case the ramp 52 is lifted off the floor and can pivot upwards in the direction shown by the arrow P of FIG. 1 so that it can pass freely over any obstacles on the floor.

To enable the shield 50 to be extended somewhat obliquely in respect of the direction of travel R, i.e., to be swivelled about a vertical axis, the double-acting units 55 can be subjected to pressure in opposite directions, i.e., one unit 55 can be extended and the other unit 55 retracted.

FIG. 4 shows a short coal face working employing a plurality of assemblies constructed as depicted in FIGS.

1 to 3. In FIG. 4, the numeral 72 is the short heading from which coal is to be won from a coal face 70 by a cutting machine. The heading 72 adjoins a roadway 71. The roof support system is in the form of a plurality of the three-frame assemblies constructed in accordance with FIGS. 1 to 3; the'individual assemblies being de-' noted A to P. The support system is brought out into the roadway 71 and the supported assemblies disposed in the roadway 71 and in the juncture zone between the roadway and the heading 72 are denoted A to-E. The face 70 takes a rectilinear course over the short heading 72 and overthe juncture between the roadway 71 and the heading 72 the face takesa curved course 73. In order to ensure that the roof of theworking will be adequately supportednot only inside the heading 72 but also in the zone'of' the roadway 71 and the entry zone, the frames of the assemblies C, D and'E, when in the basicsupportposition, are ineach case offset in relation to one another, bya distance shorter than a shifting step as shown. The staggered arrangement of the frames of the assemblies C, D and E is achieved by connectingthe springs 38 to the appropriate units 35, 36, 37'on each frame. In addition the extensible roof bars 21 of these frames C, D and Eare extended to the fullest extent, so that theyreach almost as far as the curved part of theface'73. The bars 2l of the support assemblies A and B situated in the roadway 71 are also fully extended. The frames of the assemblies A, B in the roadway7l and the frames of the assemblies F to Q in the short heading 72 are not'offsetin' relation to one another and the springs 38'may connect with the central units 36 of the frames as shown in FIG. 3.

The roof bars 21 of the frames of the assemblies F to Q in the heading 72 are retracted, although the projecting forward parts 18 of the bars 18 reach almost as far as the working face 70. I

FIG. 4 shows the initial position preceding the coal heading 72 during the cutting operation. As shown in FIG. 5, a coal cutting machine 74 is fitted with a rotatable cutting roller 75 which can be raised and lowered coal lying in front of the support system can be transferred to the conveyor 76. The coal lying on the floor immediately in front of the support system will also be pushed to the drag conveyor 76 by the clearing shields mounted on the support assemblies. As described above, the clearing shields 50 are moved forward by subjecting the units to pressure. The coal accumulated by the shields 50 can thus be taken up by the loading device 78 and loaded into the drag conveyor 76. It is possible for the loading device 78 to have a ramp structure on thestowage side, so that the clearing shields 50 push the coal over the loading ramp into the drag conveyor 76. Furthermore, by means of the clearing shields 50 the floor can be cleared in front of the individual support assemblies, so that the support can be shifted over a substantially smooth floor.

The machine 74 draws the drag conveyor 76 along behind it in the coal cutting operation. The machine 74 begins its operating movement in the roadway 71 and from here the machine 74 moves from the roadway 71 over the path 77 (FIG. 4) into the short heading 72 and thus the face 73 at the entry zoneas well as the main face 70 is cut away by the cutting depth determined by the roller 75. Immediately after the passage of the machine 74 along the path 77 the support assemblies A to E (FIG. 4) are moved forward with their bars 21 still fully extended in appropriate shifting steps i.e., commencing with the central frame and finishing with the outer frames so that the roof now exposed by the machine 74 is more or less immediately supported.

The operation of shifting the assemblies of the system support within the heading .72 can be appreciated from FIG. 5. As soon as the coal cutting machine 74 has moved past a particular support assembly, e.g., the support assembly M, the central frame-II of this assembly is first of all moved forwards after at least partial retraction of the props 1 0, 11 by pressurizing the shifting rams 62 by a shifting step, e.g., by aboutl. metre. Dur- I ing shifting of the frame IIthe unit22 is-also pressur I ized to extend the roof bars 21 of this frame II. After the props 10, -11 of the frame II are set the two outer frames I and III can then likewise be moved up into position by operating the'rams 62. This state. is shown in v frames I, III are likewise extended. The central frame II is now fed forward again by the distance corresponding to the stroke .of the rams 62 as shown in connection I in two steps of I metre each, i.e., by a total distance of cutting and FIG. 5 shows the assemblies G to P in the and which cuts to a depth of 3 metres, for example, into the working face 70. A drag conveyor 76, by which the coal detached by the coal cutting machine is conveyed machine 74 2 metres, and the'forward-extending roof bars 21 protect the roof practically as far as the working face 70.

At the end of the passage of the coal cutting machine 74 the machine 74 is moved back as far as the roadway 71, in the direction shown by the arrow S in FIG. 5, and

during this movement it pushes the drag conveyor 76 in front of it back into the roadway. As soon as the machine 74 has moved past the support assemblies on'this return journey, the individual support assemblies are shifted in the manner described by a further step of I metre as far as the working face 70, the roof bars 21 having been retracted at the same time. The support assemblies now once more occupy the position shown in FIG. 4, in which the projecting parts 18' of roof bars 18 support the roof as far as a point in the immediate vicinity of the working face 70. The same cycle of operation is repeated on the next coal cutting journey of the machine 74. It can be seen that by the sequential shifting of the support assemblies and the extension of their roof bars 21 the roof is supported, as soon as it has been exposed, over the entire length of the coal face 70 as far as the roadway 71.

FIG. 6 depicts a modified installation somewhat similar to that of FIG. and like reference numerals are used to denote like parts. In the installation of FIG. 6, the assemblies F 0 take the form shown in FIGS. 1 to 3 but the central frame II of each assembly F O has a length, i.e., in the shifting direction which is shorter by a full shifting step corresponding to the stroke of the rams 62 than the other frames I, III. The props 10, 11 of the central frame II of each assembly F O are disposed forwardly of the corresponding props 10, ll of the other frames by a full shifting step. To ensure that the roof support area is maintained, however, the rear roof bar of each central frame II has an extension 100 pivoted thereto. This extension 100 can be pivoted into a position where it is aligned with the bars 17, 18 of the frame II, as shown for the assemblies M O or into a downward stowed position as shown for the assemblies L, I.

As can be appreciated from FIG. 6 the roof support areas associated with each assembly are the same despite the relative successive shifting cycles of the individual frames. Working from left to right of the drawing will indicate the successive stages involved in advanc-' ing the assemblies towards the face 70 as the machine 74 passes across the assemblies in a cutting run or cycle. The assembly M has the forward bars 21 of its frames I, II, III all extended by a distance corresponding to a full shifting step. The bars 21 of the frames of the assemblies 0, N are fully retracted'and the rear extensions 100 of the frames II of the assemblies 0, N, M are extended by a distance corresponding to a full shifting step. In the case of the'assembly L theouter frames I, III have been shifted forward by one step'in relation'to the assembly M, while their bars 21 aremaintained in position. The forward bars 21 of the central frame II of the assembly L' has however been extended by a further shifting step to maintain alignment with the bars 21 of the outer frames 1, III. The rear extension '100 of the frame ll of the assembly L is in a stowed position. In the case of the assembly K the frame II has been shifted forward by one step in relation to the assembly L. In this case the forward bars 21 of the frame II is retracted by one shifting step to correspond to the bars 21 of the outer frames I, II and the rear extension 100 of the frame II is now extended. The assemblies I, H, G and F have their outer frames I, ll again moved up by the shifting step and correspond to the assembly L.

We claim:

I. In a mine roof support assembly composed of relatively displaceable frames, each frame having telescopic props supporting a roof cap and resilient means interconnecting the bases of the props, and guiding and shifting means operably disposed between adjacent pairs of frames for effecting relative displacement of the frames and the improvement comprising a plurality of connection units provided on the resilient means of each frame and spaced apart longitudinally thereof and in the direction of said relative displacement, each connection unit enabling connection to be made between connected to selected ones of the connection units of the adjacent pair of frames.

2. An assembly according to claim 1, wherein the props of each frame are each supported by a floorengaging skid and the resilient means interconnects the skids.

3. An assembly according to claim 2, wherein the resilient means of each frame is in the form of two parallel leaf springs disposed one above the other.

4. An assembly according to claim 1, wherein leaf springs extending transversely of the direction of displacement of the frames serve to connect said selected connection units to the guiding and shifting means.

5. An assembly according to claim 4, wherein the units have vertical cotter pins which lock a U-shaped member connected to the transverse leaf springs to the selected units.

6. An assembly according to claim 1, wherein the roof cap of each frame has at least one extendible and retractable roof bar at its forward end, which in use is disposed adjacent a mineral face.

7. An assembly according to claim 6, wherein the extendible roof bar is operated by a piston and cylinder unit.

8. An assembly according to claim 1, wherein a rubble deflector is suspended from the rear end of the roof caps of the frames. 7

9. An assembly according to claim 8, whereinthere is further provided a guard shield disposed at the rear end of the frames, the guard shield having side walls which project alongside the rear props of the outermost frames.

10. An assembly according to claim I, wherein each guiding and shifting'means includes a ram operable to effect the relative displacement of the frames.

11. An assembly according to claim 10, wherein each guiding and shifting means further comprises two guide elements disposed within a protective housing and extending in the direction of displacement and a guide piece mounted for sliding along the elements and the housing, the guide piece being connected to one of the selected connected units on one frame and the housing being connected to another of the selected units on an adjacent frame with the rams being connected between the housing and the rear prop of said one frame.

12. An assembly according to claim 1, wherein three frames are provided each having two props the central frame being shorter in length, in the direction of relative displacement, than the outer frames by a distance corresponding to a shifting step so that when the frames are arranged side-by-side with the forward ends of their roof caps aligned the props of the central frame are disposed forwardly of the corresponding props of the outer frames by said distance, there being further provided an extendible roor bar at the rear end of the roof cap of said central frame which, when extended, compensates for said difference in length between the frames.

13. An assembly according to claim 1, wherein there is further provided a clearing shield disposed at the forward end of the assembly and means for moving the shield outwardly in relation to said frames.

14. An assembly according to claim 13, wherein the shield has a body disposed in a substantially upstanding position and a ramp pivotably connected to said body to move about an axis extending transversally of the ditowards the floor. rection of displacement and engageable, during use, with the floor of a mine working.

15. An assembly according to claim 14, wherein the ramp has webs which are engageable on the rear side 5 dunng movementof the body to limit the pivotal movement of the ramp 16. An assembly according to claim 14, wherein there is further provided means for guiding said shield 

1. In a mine roof support assembly composed of relatively displaceable frames, each frame having telescopic props supporting a roof cap and resilient means interconnecting the bases of the props, and guiding and shifting means operably disposed between adjacent pairs of frames for effecting relative displacement of the frames and the improvement comprising a plurality of connection units provided on the resilient means of each frame and spaced apart longitudinally thereof and in the direction of said relative displacement, each connection unit enabling connection to be made between the resilient means and the associated guiding and shifting means with each guiding and shifting means being connected to selected ones of the connection units of the adjacent pair of frames.
 2. An assembly according to claim 1, wherein the props of each frame are each supported by a floor-engaging skid and the resilient means interconnects the skids.
 3. An assembly according to claim 2, wherein the resilient means of each frame is in the form of two parallel leaf springs disposed one above the other.
 4. An assembly according to claim 1, wherein leaf springs extending transversely of the direction of displacement of the frames serve to connect said selected connection units to the guiding and shifting means.
 5. An assembly according to claim 4, wherein the units have vertical cotter pins which lock a U-shaped member connected to the transverse leaf springs to the selected units.
 6. An assembly according to claim 1, wherein the roof cap of each frame has at least one extendible and retractable roof bar at its forward end, which in use is disposed adjacent a mineral face.
 7. An assembly according to claim 6, wherein the extendible roof bar is operated by a piston and cylinder unit.
 8. An assembly according to claim 1, wherein a rubble deflector is suspended from the rear end of the roof caps of the frames.
 9. An assembly according to claim 8, wherein there is further provided a guard shield disposed at the rear end of the frames, the guard shield having side walls which project alongside the rear props of the outermost frames.
 10. An assembly according to claim 1, wherein each guiding and shifting means includes a ram operable to effect the relative displacement of the frames.
 11. An assembly according to claim 10, wherein each guiding and shifting means further comprises two guide elements disPosed within a protective housing and extending in the direction of displacement and a guide piece mounted for sliding along the elements and the housing, the guide piece being connected to one of the selected connected units on one frame and the housing being connected to another of the selected units on an adjacent frame with the rams being connected between the housing and the rear prop of said one frame.
 12. An assembly according to claim 1, wherein three frames are provided each having two props the central frame being shorter in length, in the direction of relative displacement, than the outer frames by a distance corresponding to a shifting step so that when the frames are arranged side-by-side with the forward ends of their roof caps aligned the props of the central frame are disposed forwardly of the corresponding props of the outer frames by said distance, there being further provided an extendible roor bar at the rear end of the roof cap of said central frame which, when extended, compensates for said difference in length between the frames.
 13. An assembly according to claim 1, wherein there is further provided a clearing shield disposed at the forward end of the assembly and means for moving the shield outwardly in relation to said frames.
 14. An assembly according to claim 13, wherein the shield has a body disposed in a substantially upstanding position and a ramp pivotably connected to said body to move about an axis extending transversally of the direction of displacement and engageable, during use, with the floor of a mine working.
 15. An assembly according to claim 14, wherein the ramp has webs which are engageable on the rear side of the body to limit the pivotal movement of the ramp towards the floor.
 16. An assembly according to claim 14, wherein there is further provided means for guiding said shield during its movement. 